Thermoplastic elastomers are known. They have many of the properties of thermoset elastomers, yet they are processable as thermoplastics. One type of thermoplastic elastomer is a thermoplastic vulcanizate, which may be characterized by finely-divided rubber particles dispersed within a plastic. These rubber particles are crosslinked to promote elasticity.
Layered mineral clays, such as smectite clays, have been integrated to form polymer-clay nanocomposites. These nanocomposites have included thermoplastic nanocomposites such as those prepared from nylon and montmorillonite clay. Thermoset nanocomposites have also been developed that include, for example, functionalized rubbers.
In an attempt to make useful thermoplastic vulcanizate nanocomposites, thermoplastic vulcanizates have been prepared as reported by Thakkar et al., Paper No. 25, Rubber Division, American Chemical Society, 2003. According to this teaching, rubber, extender oil, cure activator, and silicate nanoclay were compounded at low temperatures within a first mixing stage. Once compounded, dynamic vulcanization was effected in a second stage mix at elevated temperatures with polypropylene to form a thermoplastic vulcanizate. It was reported that the presence of the smectic clay diminishes the cure of the EPDM rubber, thereby requiring an increase in the cure system concentration to maintain crosslink density.
A desire therefore remains for a technologically useful thermoplastic vulcanizate including layered mineral clays and/or thermoplastic vulcanizate nanocomposites.